Free piston engine bounce compressor

ABSTRACT

An improved free piston engine is disclosed with an improved bounce compressor which includes a bounce compressor cylinder and a bounce compressor piston reciprocally movable with respect to each other. The engine includes venting means for the bounce compressor cylinder which provides a limited high velocity ejection of fluid from such cylinder at a location and in a manner adapted to insure regular periodic removal of contaminants from a bounce chamber within said cylinder. In one embodiment, passage means formed in the bounce compressor piston and bounce compressor cylinder, and check valves positioned in the bounce compressor piston, allow the controlled venting of the air contained within the bounce compressor chamber during a portion of the bounce compressor cycle and allow uncontaminated air to be introduced into the bounce chamber during another portion of the bounce compressor cycle, so as to minimize the contaminants in the bounce chamber. Alternate embodiments are also shown which similarly permit contaminants or contaminated air in the bounce chamber to be vented.

United States Patent Braun 1541 FREE PISTON ENGINE BOUNCE COMPRESSOR [72] Inventor: Anton Braun, 6421 Warren Ave.,

Minneapolis, Minn. 55435 [22] Filed: March 4, 1970 [21] Appl. No.: 16,377

[52] US. Cl ..417/491, 123/46, 267/65 R, 267/124, 417/341, 417/521, 417/526, 417/530, 417/535 [51] Int. Cl ..F02b 71/00, F04b 7/04, F04b 21/94 [58] Field of Search ..267/65 R, 124; 123/46; 417/490, 491, 492, 495, 521, 526, 530, 534, 535, 536, 537, 341

[56] References Cited UNITED STATES PATENTS 2,025,177 12/1935 Pescara ..417/341 2,189,497 2/1940 Pescara ..123/46 R13,949 7/1915 Davis ..417/491 1,128,643 2/1915 Wetmore ..417/495 2,787,223 4/1957 Sargent ..417/526 X 2,989,001 6/1961 Wilkenloh et a1 ..417/526 X Primary Examiner-Gerald M. Forlenza Assistant Examinerl-loward Beltran Attorney-Frederick E. Lange, William C.- Babcock and John J. Held, In

[ 1 Sept. 26, 1972 7 ABSTRACT ln one embodiment, passage means formed in the bounce compressor piston and bounce compressor cylinder, and check valves positioned in the bounce compressor piston, allow the controlled venting of the air contained within the bounce compressor chamber during a portion of the bounce compressor cycle and allow uncontaminated air to be introduced into the bounce chamber during another portion of the bounce compressor cycle, so as to minimize the contaminants in the bounce chamber. Alternate embodiments are also shown which similarly permit contaminants or contaminated air in the bounce chamber to be vented.

18 Claims, 5 Drawing Figures LOL ROL 51 l- 1 i i i 1 1 V sog RcE 5 18 14 24 FLUID 4a 1 v /T 22 FLUID ARGE a n DISCH PATENTEDsms I972 3.694.1 l 1 sum 2 [IF 2 a! I I FLUID FLUID DISCHARGE SOURCE OF FREE PISTON ENGINE BOUNCE COMPRESSOR BACKGROUND This invention relates to free piston engines generally, and specifically to improved free piston engines having special bounce compressor features.

In the past, free piston engines have utilized bounce compressors to provide the control necessary to allow the engine to operate over a wide range of operating conditions and to provide all or part of the energy necessary to return a power piston within the engine to a position where repetitive combustion may occur and sustained operation of the engine is possible.

These bounce compressors suffered from the disadvantage of containing a more or less trapped or stale air or gas charge which may become fouled by lubricating oil or other contaminants. Such a bounce compressor thus may present a problem in controlling the free piston engine or at least a risk of explosive or other damage to the engine. The exact time or effect of such fouling on the bounce compressor is unpredictable, being dependent on the nature and degree of fouling and of the charge. Thus, a generally uncontrolled pressure build-up may occur as a result of the fouling. An uncontrolled pressure build-up may result in a loss of control, in itself. Moreover, I have found that serious damage may also result if the contamination and repeated compression in the bouncer compressor gradually provides a combustible mixture of lubricating oil particles and air in the bounce compressor chamber. Such a mixture may be self-ignited on a compression stroke within the bouncer. The resulting explosive combustion can release energy far in excess of that for which the engine housing and parts would otherwise need to be designed.

Some prior engines have included means for opening a bounce chamber to the atmosphere at or near the end of a stroke where the bounce chamber has its maximum volume. These arrangements are not believed, however, to insure controlled and thorough removal of contaminants in a positive manner at each stroke.

SUMMARY The improved free piston engines of the present invention solve the above problems of free piston engines with bounce compressors by using novel means to vent the bounce compressor chamber while retaining the desired operating and control characteristics of the bounce compressor.

Specifically, the engine includes venting means for the bounce compressor cylinder which provides a limited high velocity ejection of fluid from such cylinder at a location and in a manner adapted to insure regular periodic removal of contaminants from a bounce chamber within said cylinder. Briefly, the free piston engines of the present invention utilize a bounce compressor which includes a specially located passage or valve means to allow a portion of the air or other gas within the bounce compressor chamber to escape at high velocity during a limited controllable portion of each cycle, and means to supply uncontaminated air or other gas into the chamber of the bounce compressor. Thus, the contaminants are periodically carried away with the escaping air or gas without adversely affecting basic desired bounce compressor characteristics. Additional valve means may also be provided to control the entrance of the fresh air or gas from a pressurized source to the bounce compressor chamber during an appropriate portion of the cycle. Thus, a small portion of bounce compressor air or gas is vented to remove or carry with it its undesired contaminants and the escaped air or gas is replaced by a new supply of air or gas through the additional valve means. Specific embodiments of the present invention present a venting arrangement which incorporates one or more slots or passages of carefully predetermined location and cross section in the bounce compressor, and particularly a venting passage in the lower cylinder wall of the bounce compressor.

It is accordingly one object of the present invention to provide for the venting of a bounce compressor of a free piston engine to change the air or gas within the bounce compressor in such a manner as to effectively carry away contaminants with the vented air or gas.

It is another object of the present invention to provide a simple venting arrangement which operates automatically to provide high pressure venting at predetermined positions of a bouncer compressor piston.

The manner in which these and other objects and ad vantages are achieved will be apparent from the following detailed description of illustrative and preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, which form a part of this application,

FIG. I is an enlarged schematic, vertical, cross-sectional view'of a vented bounce section which is part of the free piston engine of FIG. 4 and is constructed according to the present invention, the venting means including a passage and valve in the bounce piston itself;

FIG. 2 is a pressure versus volume curve which is useful in explaining the teachings of the present inven tion;

FIG. 3 is a partial, vertical, schematic, cross-sectional view of another embodiment of a bounce section using the teachings of the present invention;

FIG. 4 is a partial schematic view of an improved free piston engine employing the vented bounce section of FIG. 1 according to one form of the present invention; and

FIG. 5 is a view, similar to FIG. 4, of another free piston engine which incorporates the vented bounce section of FIG. 3.

Where used in the various figures of the drawings,

the same numerals designate the same or similar parts. Furthermore, when the terms right," left," right end, and left end" are used herein, it should be understood that these terms have reference only to the structure shown in the drawings as it would appear to a person viewing the drawings and are utilized only to facilitate describing the invention.

DESCRIPTION In FIG. 1, a bounce section generally designated at 10 is shown having a generally cylindrical housing 12 with a bounce cylinder 14 formed therein. Housing 12 is closed at its left end by an end wall 15 and has its right end attached to another free piston engine part 17. The housing 12 and part 17, in the form shown in detail in FIG. 1, form a power piston and a compressor piston for a free piston engine which is more fully shown and explained in relation to FIG. 4. For purposes of illustration, the engine is similar to that shown in US. Pat. No. 2,025,177 to Pescara.

A bounce compressor piston generally designated at 18 is arranged within housing 12 for relative reciprocal movement with respect to housing 12 in directions parallel to the longitudinal central axis of bounce cylinder 14, in both relative leftward and rightward directions. (For convenience in explanation, the piston is herein said to move with respect to the bounce cylinder housing 12. It will be understood, however, that in the-embodiment of FIGS. 1 and 4, where the bounce chamber is inside the power piston, the bounce piston is actually fixed in position and the combination power piston and bounce cylinder does the moving. On the other hand, in the device of FIG. 5, the bounce cylinder is fixed and the bounce piston is the part which actually moves.) Bounce compressor piston 18 is shown as a piston having a left face 20, a right face 22, and a generally cylindrical sidewall 23 interconnecting faces 20 and 22. Bounce piston 18 may move leftward with respect to housing 12 from the position shown in FIG. 1 until left face 20 reaches a point in the cylinder 14 indicated by the line LOL which is the left operational limit of the bounce piston. Bounce piston 18 may then return rightward with respect to housing l2until right face 22 reaches a point in the bounce cylinder 14 indicated by the line ROLT which indicates the right operational limit of the bounce piston.

A connection means or member 24 is shown as integrally formed with piston 18 and extending rightward through an aperture 26 formed within a wall 28 closing the right end of housing 12. Conventional shaft seals 30 are positioned in aperture 26 to minimize the leakage of gas and lubricant between member 24 and aperture 26 upon the reciprocation of member 24.

As bounce piston 18 reciprocates within cylinder 14 of FIG. 1, two chambers 32 and 34 are defined. Chamber 32 is defined in bounce cylinder 14 between the left face 20 of bounce piston 18 and the right face 36 of end wall 15. Chamber 34 is defined in cylinder 14 between the right face 22 of bounce piston 18 and the left face 37 of wall 28. I

In order to provide venting means for the bounce chamber 32, two generally tubular passages 38 and 40 are formed in member 24. The left end of passage 38 communicates with chamber 32 by means of a one-way control valve means or check valve assembly generally designated as 42 formed in an axially extending cavity 43 in piston 18.

Check valve 42, which only allows the ingress of fluid into chamber 32, includes a ball 44, a valve spring.46, and a threaded retaining ring 48. The other end 50 of passage 38 is designed to be connected to a source of pressurized fluid 51, as shown. Fluid source 51 is shown in FIGS. 1 and 4 as separate from free piston engine 16. However, fluid source 51 may be a chamber within the free piston engine, the atmosphere, or a source of pressurized fluid outside the free piston engine.

The left end of passage 40 communicates with a generally annular chamber 52 which is defined between the bounce cylinder 14 and the side wall 23 of bounce piston 18. The left and right extremities of the annular chamber 52 are defined by a left sealing ring 54 and a right sealing ring 56 carried by grooves formed in bounce piston 18 to control fluid flow between the bounce piston 18 and bounce cylinder 14, i.e., to minimize the leakage of gases between the bounce piston 18 and the bounce cylinder 14 as the bounce piston 18 reciprocates within the bounce cylinder 14. A one-way control valve means or check valve assembly generally designated as 58 is formed in a radially extending second cavity 59 in piston 18 extending between the left end of passage 40 and the chamber 52. Cavity 59 has a firstv end opening into chamber 52. Check valve assembly 58, which only allows the egress of fluid from chamber 52, includes a ball 60, a valve spring 62, and a threaded retaining ring 64. The other end 66 of passage 40 is adapted to be connected to a fluid discharge region, designated as 67, which again is shown as separate from engine 16 but may be a chamber within the engine, the atmosphere, or other region outside the engine.

The venting and control means of this embodiment include venting passages 68 and 70, positioned in the housing 12. Specifically, one or more venting passages 68, one of which is shown in FIG. 1, are positioned around the circumference of and within the cylindrical side walls of housing 12 so as to form one or more slots in bounce cylinder 14 which provide controlled fluid communicationbetween chamber 32 and chamber 52 during a limited intermediate portion of the stroke, just before the bounce piston 18 nears the left operational limit. Thus, slots 68 must be of proper depth within housing 12 and appropriate width along the circumference of cylinder 14 to provide the necessary but limited fluid communication, as will be discussed hereinafter. Slot 68 must similarly be of a sufficient length along the longitudinal axis of cylinder 14 which length must at least exceed the length of sealing ring 54 to bypass sealing ring 54. The length of slot 68 in this embodiment must not, however, exceed a length equal to the distance between sealing rings 54 and 56 added to the width of sealing rings 54 and 56, so as not to bypass both sealing rings 54 and 56, for reasons that will become clear hereinafter. Thus, slot 68 provides a venting passage which opens into and connects two axially spaced portions of the cylinder. As bounce piston 18 moves leftward from its right operational limit, sealing ring 54 passes over slot 68 to provide fluid comm unication between cavity 59 of fluid discharge passage 40 and bounce chamber 32, by way of valve 60, annular chamber 52, and venting slot 68. The total cross section of venting passages 68 is relatively restricted, so that limited fluid communication is provided between chamber 52 and chamber 32 without undesired loss of pressure in bounce chamber 32 and without disturbing the normal engagement of ring 54 with the inner sur face 14 of the cylinder.

Similar valve means or venting passages 70 may be formed within the sidewalls of housing 12, so as to form slots within bounce cylinder 14 adjacent to the right operational limit of piston 18 and longitudinally spaced from slot 68. As bounce piston 18 moves rightward from its left operational limit, sealing ring 56 passes over slot 70, and sealing ring 56 is bypassed to provide fluid communication between chamber 52 and chamber 34 without disturbing ring 56. Thus, slots 70 provide limited communication axially between chamber 52 and chamber 34 during a portion of the stroke near the right operational limit of bounce piston 18 to vent chamber 34 to the fluid discharge passage 80 in a similar fashion to the manner in which slots 68, chamber 52, valve 60 and cavity 59 vent chamber 32.

Another passage or slot 72 is formed within the left face 37 of wall 28 to provide communication between chamber 34 and the atmosphere through a check valve assembly 74 comprising a threaded retaining ring 76, a ball 78, and a valve spring 80. Check valve assembly 74 serves as a one-way valve means which only allow ingress of air or gas into chamber 34 similarly to the fashion that valve means 42 only allows ingress of air or gas into chamber 32.

OPERATION mal bounce compressor with two exceptions. First, just before the bounce piston nears its left operational limit and the pressure in the bounce chamber is nearing its highest limit, the bounce chamber is vented for a limited short portion of the piston stroke to allow a small portion of the air or gas in the bounce compressor chamber to escape at relatively high velocity and thus carry away a portion of the contaminants in the bounce chamber during each cycle. Secondly, just before the bounce compressor piston nears its right operational limit and the pressure in the bounce compressor is approaching its lower limit, a fresh uncontaminated supply of air or gas is allowed to enter the bounce compressor chamber. By this venting and replenishing of the air within the bounce compressor chamber, the range of pressure obtainable from the bounce compressor is somewhat reduced, since there may be little or no pressure rise or even a small pressure drop during the time the bounce compressor chamber is being vented at high pressure, nor can there be the normal pressure decrease during the time a new supply of air is being provided to bounce the compressor chamber. However, a range of pressure sufficient to provide the control requirements of the engine is yet possible through proper design.

Specifically, with respect to the embodiment of the present invention shown in FIGS. 1 and 4 and the explanatory, idealized, pressure-volume curve for chamber 32 shown in FIG. 2, the operation is as follows. Point I on the curve of FIG. 2 occurs when the pressure is the least and the volume is the greatest in chamber 32. Point 1 then corresponds to the time when piston 18 is at its right operational limit. As piston 18 moves leftward from its right operational limit towards its left operational limit, the volume within chamber 32 decreases and the pressure within chamber 32 increases as shown on the curve between points 1 and 2.

At point 2, sealing ring 54 is positioned over the right edge of slot 68 in a manner that sealing ring 54 is bypassed and chamber 32 can communicate with chamber 52. By proper design and proper selection of the total cross section of passages 68 and of the valve spring 62 of the valve assembly 58, the force applied to the ball 60 by the pressure differential between chamber 32 and the discharge region 67 at point 2 of the curve can overcome the retarding force of spring 62, push ball 60 back from its seat on retaining ring 64, and allow air to escape from chamber 32, through slot 68, through chamber 52, through check valve assembly 58, through passage 40, and enter the fluid discharge region 67. Since chamber 32 is being vented during the time sealing ring 54 passes over the length of slot 68, the volume of chamber 32 is decreasing but there may be no pressure rise in chamber 32 during that portion of the stroke. This is illustrated by the flat portion of the idealized curve between point 2 and 3. As piston 18 continues to move leftward towards-its left operational limit, sealing ring 54 passes beyond the left edge of slot 68 and the pressure in chamber 32 again begins to rise as the volume in chamber 32 is decreased. This phase of operation is illustrated between points 3 and 4. The piston 18 then reaches its left operational limit and reverses direction to move rightward within cylinder 14. Until sealing ring 54 again reaches slot 68, pressure decreases within chamber 32 as the volume of chamber 32 increases along line 4-3 in FIG. 2. As sealing ring 54 again reaches the left edge of slot 68, chamber 32 may again be vented through passage 40. Since valve spring 62 was chosen with the pressure at point 3 in mind, however, no further venting of chamber 32 takes place, and the pressure in chamber 32 continues to decrease along curve 3-5 in FIG. 2. At point 5 of the curve, the pressure differential across check valve as sembly 42 exceeds the preselected retarding force of valve spring 46 and a fresh supply of air enters chamber 32 from fluid source 51, through passage 38, and check valve assembly 42. The entrance of this fresh supply of air prevents any substantial further pressure decrement in chamber 32 as the volume continues to increase. Thisis illustrated by the flat portion of the idealized curve between point 5 and point 1.

As also shown in FIG. 2, if the total cross section of passage 68 is larger, or if the pressure setting for opening check valve 60 is lower, there could be a loss of bounce chamber pressure as shown by dotted line 2- 3A, with corresponding to in the remainder of the pressure curve from 3A TO 4A to 5A, etc. A more restricted venting passage or shorter venting period could similarly vary the pressure curve 234-5 on the higher pressure side. The important thing is to retain sufficient pressure at point 4 for the desired bounce chamber control and to achieve the desired venting at a velocity and in a manner designed to spit out" any liquid or other contaminants from the bounce chamber.

Thus, this bounce compressor chamber 32 is vented by slot 68, and the venting is piston controlled so that only a small portion of the air within chamber 32 escapes. This limited, high-velocity venting of a portion of the air within chamber 32, of necessity, carries a portion of the contaminants within chamber 32 with it to continually purge chamber 32 of contaminants. Since the air supply within chamber 32 is replenished during each cycle, predictable repetitive operation bf the bounce compressor may be achieved, and the danger of explosive damage is minimized.

It may now be seen that chamber 34 is similarly vented through a similar venting passage or slot 70, check valve assembly 58, and passage 40, just before the piston 18 nears its right operational limit, as slot 70 bypasses sealing ring 56 and briefly connects chambers 52 and 34. A fresh supply of air is supplied to chamber 34 during each cycle through check valve assembly 74, when the pressure differential across check valve 74 exceeds the preselected retarding force of valve spring 80 in a similar fashion to that explained in relation to chamber 32 and check valve assembly 42. The exact duplication ofthe venting for chamber 32 is not necessary for chamber 34; however, some venting -or replenishing of air of chamber 34 is necessary, if it is desired to prevent uncontrolled pressure from existing in'chamber 34.

As shown more fully in FIG. 4, part 17 forms a compressor piston within engine 16. Compressor piston 17 reciprocates within a compressor cylinder 100 formed within a housing 102 of engine 16 to define a compressor chamber 104 between a right face 106 of compressor piston 17 and a left face 108 of an end wall 110 of housing 102. Another chamber 112 is defined leftward of the left face 114 of compressor piston 17, which chamber communicates with the atmosphere through an aperture 116 formed in housing 102 adjacent chamber 112.

Conventional intake valves 118, two of which are schematically shown in compressor piston 17, provide air from the atmosphere entering chamber 112 through aperture 116 to compressor chamber 104. After being compressed by compressor piston 17, the air is forced through conventional exhaust valves, one of which is schematically shown at 120, and to a receiver 122 for use.

g A 'power cylinder 124 is also formed within housing 102 and cylindrical housing 12 of FIG. 1 forms apower piston 12 which reciprocally moves within power cylinder 124. A left face 126 of end wall 15 of cylindrical housing 12 of FIG. 1 forms a power face 126 of power piston 12. A chamber 128, leftward of power face 126, is the chamber in which combustion occurs to provide power for the engine. Power face 126 and power piston 12 are shown in FIG. 4 at the outer-deadpoint of the engine, which point conforms to the bottom-dead center in a crank type engine, with the exhaust ports 130 shown exposed.

In FIG. 4, with power face 126 of power piston 12 at the outer-dead-point, as shown, bounce piston 18 is at the left operational limit (LOL) of FIG. 1. Energy stored in the compressedair within chamber 32 of' bounce section and in compressor chamber 104 forces power piston 12 leftward to provide the next compression stroke of the free piston engine 16. Leftward movement of power piston 12 also causes bounce piston 18 to move relatively with respect to wall from its left operational limit towards its right operational limit ROL) within cylinder 14 to provide a pressurestroke relationship as shown along the line 45 in FIG. 2. During this leftward movement of power piston 12, chamber 34 is vented through valve 58 when piston ring 56 passes over slot 70 formed within cylinder 14, as explained with respect to FIG. 1. Upon completion of the compression stroke of power piston 12, piston 18 is located at its right operational limit within and rela tively to cylinder 14, and combustion of gases in chamber 128 forces power piston 12 rightward on its power stroke to thus cause bounce piston 18 to move from its relative right operational limit towards its left operational limit along line 1-2 in FIG. 2. During this movement, bounce chamber 32 is vented through valve 58 as piston ring 54 passes over slot 68. During this same stroke, a fresh charge is provided for chamber 34 through valve 74 at the appropriate time. At the completion of the power stroke, the energy stored in the compressed air within chamber 32 and compressor chamber 104 again urges power piston .12 leftward to repeat the cycle, and a fresh charge is provided for chamber 32 through valve 42 at the appropriate time.

Since the operation of the remaining half of engine 16 shown in FIG. 4 is identical to that just described, with mirror image symmetry, no explanation of this remaining half is included. Also, while the source of fluid 51 is shown in FIG. 4 as an air pressure source outside of engine 16, source 51 may as well be the compressor chamber 104 of engine 16. Further, while fluid discharge region 67 is shown as a separate entity, it may as well be the atmosphere or the intake duct of the compressor.

The embodiment of the present invention shown in FIGS. 3 and 5 operates in a similar fashion to the embodiment of FIGS. 1 and 4 except that the embodiment shown in FIG. 3 is a venting arrangement which does not require passages or valves within the piston, thereby further illustrating the basic operation of the present invention. As shown in detail in FIG. 3, the slot 68 is formed of such length as to bypass both sealing ring 54and sealing ring 56 as the piston 18 travels between its right operational limit and its left operational limit. g

The venting of chamber 32 is thus accomplished by way of passage 68, chamber 52 and annular chamber 34 during the portion of the swept stroke of piston 18 where slot. 68 does so connect chamber 32 and chamber 34. As shown in FIG. 5, there is a specific check valve assembly 42 providing a fresh supply of air to chamber 32. Thus, the basic function of purging bouncer compressor chamber 32 of contaminants will be achieved.

For purposes of illustration, the free piston engine shown more fully in FIG. 5 is similar to that shown in Pat. No. 2,l89,497 to Pescara. In FIG. 5, cylindrical housing 12 and part 17 form a part of housing 102 of free. piston engine 25. Bounce piston l8 then reciprocates with respect to housing 102 within bounce cylinder 14, and connection member 24 connects bounce piston 18 to a compressor piston designated 150. Connection member 24 is of small enough diameter with respect to cylinder 14 to provide annular chamber or passage 34 communicating between venting passage 68 and compressor chamber 154 when the parts are in the position of FIG. 5. Compressor piston reciprocates within a compressor cylinder 152 to define the compressor chamber 154 between the left face 156 of compressor piston 150 and the housing wall part 17 of FIG. 5.

Another chamber 158 is defined rightward of the right face 160 of compressor piston 150 which chamber communicates with the atmosphere through an aperture 162. Conventional intake valves, two of which are schematically represented at 164, provide air from the atmosphere entering chamber 158 through aperture 162 to compressor chamber 154. After being compressed by compressor piston 150, the air in chamber 154 is forced through conventional exhaust valves, one of which is shown schematically at 166, and to a receiver 168 for use.

A power cylinder 170 is also formed within housing 102, and a power piston 172 reciprocally moves within power cylinder 170 to define one end of a combustion chamber 174. In the embodiment of the present invention shown in FIG. 5, with the power piston 172 at its outer-dead-point as shown, piston 18 within bounce section 10 is at its left operational limit (LOL) within and relative to cylinder 14.

In the position shown in FIG. 5, the energy stored in the compressed air within chamber 32 and compressor chamber 154 forces power piston 172 rightward to begin its compression stroke. During this stroke, as compressor piston also moves rightward, air will enter chamber 154 through opening 162, chamber 158 and valves 164. This rightward movement of power piston 172 also causes the bounce piston 18 to move from its left operational limit towards its right operational limit (ROL).

When combustion occurs in chamber 174, the power piston 172 and connected parts will be driven back to the left. During this leftward movement of power piston 172, chamber 32 is briefly vented by means of venting passage or slot 68 during the limited portion of the stroke when sealing rings 54 and 56 are bypassed by slot 68 as in the position of FIG. 3. At that time, passage 68 interconnects chamber 32 with chamber 34 and compressor chamber 154 to provide for the splitting out of a limited amount of air or gas and thus to carry out liquid or other contaminants to chamber 154 and ultimately out through valve 166.

Passage 68 is then closed when sealing ring 54 moves beyond it to the left during final compression in the ounce chamber 32. On the next return stroke to the right when the pressure inv chamber 32 drops to a predetermined point, a fresh charge of air is provided to chamber 32 through one-way valve 42; which is shown in the embodiment of FIG. 5 as attached to the exterior of housing 12, rather than within piston 18, as in FIGS. land 4.

Upon the completion of each rightward compression stroke of power piston 172 and with powerpiston 18 at its right operational limit, combustion within chamber 174 initiates thepower stroke of engine 16 to the left. Power piston 172 and hence bounce piston 18 then move leftward to thus move bounce piston 18 from its right operational limit towards its left operational limit. Chamber 32 is again vented as slot 68 bypasses both sealing rings 54 and 56 to provide fluid communication between chamber 32 and compressor chamber 154.

Further travel of power piston 172 leftward brings the interconnected bounce piston 18 to its left operational limit, whereupon the energy stored in the compressed air or gas within chamber 32 and compressor chamber 154 again forces powerpiston 172 and the attached bounce piston 18 rightward to repeat the cycle.

Again, the remaining half of engine 25 is symmetrical to that already explained and the operation thereof need not be explained further. It is to be noticed that in this embodiment, the source of air or gas for replacing that which escapes during venting of the bounce chamber is taken to be the atmosphere, e.g., through valve 42A shown in FIG. 5, and the fluid discharge region is taken to be compressor chamber 154.

Also, it is to be noted that the specific embodiment shown in FIG. 1 or parts thereof may be used in place of the construction of FIG. 3 in a free piston engine of the type shown in FIG. 5 with limited changes in construction, for example, with end 50 of passage 38 F IG. 1) communicating with compressor chamber 154 (FIG. 5) through an appropriate opening in the side of member 24, and with end 66 of passage 40 (FIG. 1) communicating with chamber 158 (FIG. 5) through an appropriatev opening in the side of power piston 172 close to face 160.

Now that the basic teachings of the present invention have been explained, many other extensions and variations will be obvious to one having ordinary skill in the art. For example, many types of valves other than the ball check valve assemblies shown may be used according to the teachings of the present invention.

Also, while piston rings have been shown as the means sealing the bounce chamber 32, other types of sealing means may be used with the teachings of the present invention. Such sealing means may be labyrinth seals or close tolerance sealing between the bounce piston 18 and the bounce cylinder 14.

Furthermore, it will be noted that the preferred embodiment of the invention takes advantage of the high pressure generated within the bounce chamber itself, and also of the scraping effect of the bounce piston within the bounce cylinder walls. Thus, in FIGS. 1 and 3, the venting passage 68 is located at a lower inner surface of the bounce cylinder, i.e., the surface to which fluid or solid contaminants would normally flow by gravity. The venting passage is also located at a point which is passed by the lower inner edge of the bouncer piston. Thus, oil or other liquid or contaminants which might be on the inner surface of the bounce cylinder will be scraped along by the edge of the piston to the immediate location of the venting passage, so that these contaminants will be in position to be forced out through the passage when the piston ring reaches a position which effectively opens such passage. In this arrangement, the air or gas to be vented from the bounce compressor chamber cannot escape without actually carrying with it, or pushing ahead of it, some of the undesiredcontaminants.

It will be apparent, however, that the invention may take other forms in which, for example, compressed air or gas is injected from a source other than the bounce chamber itself and/or in which the shape and relative location of the parts, including the venting passage, provides a sweeping or scavenging action within the bounce chamber in somewhat the same manner'as the well known scavenging methods which are adapted to remove exhaust gases from power cylinders in such engines.

It can also be seen from FIG. 2 that if the desirable amount of venting becomes so large as to have an appreciable effect on efficiency, the energy lost could at least partially be regained by venting" the air from the high pressure vent into the compressor or scavenge pump at an appropriate pressure level. Also, the amount of venting air or gas may be increased purposely to achieve a cooling effect in the bounce chamber. This could be of particular value in cases where wall 15 represents a portion of the power piston, such as for instance in FIG. 4.

In the preferred embodiments shown herein, the venting passage is opened to the bounce chamber only during the last half of the relative movement or stroke of the bounce piston in the direction of increasing pressure in the bounce chamber, i.e., the last half of the stroke as the piston is on its way to the top (i.e., high pressure) dead center position of the bouncer.

The foregoing specification accordingly describes the background and nature of the invention and some of the ways of practicing it, including those embodiments presently contemplated as the best mode of carrying out the invention.

What is claimed is:

1. In a free piston engine, a bounce compressor including a bounce cylinder, a bounce piston within the bounce cylinder and defining at least one bounce chamber therein, one of the bounce cylinder and bounce piston being operatively connected to the engine whereby the bounce cylinder and bounce piston are relatively and reciprocally movable with respect to each other to provide desired control requirements of the engine during operation, and improved venting and control means for said bounce chamber, said venting and control means including venting passage means of restricted cross section, and fluid controlling means selectively opening said ventingpassage means to said bounce chamber during only a limited portion of that half of the relative reciprocal movement of said piston and cylinder in which the bounce chamber pressure has increased, the venting passage means and fluid controlling means having a construction and relative arrangement and location providing, during said limited portion of movement, a brief, controlled high-velocity ejection of a small portion of fluid from said chamber through said venting passage means at a velocity and location providing effective removal of contaminants from said chamber with said fluid while maintaining sufficient compression pressure in the bounce chamber at the end of a bounce compression stroke to provide desired control requirementsof the engine, and means for replacing the ejected fluid. I

2. A free piston engine according to claim 1 in which said means for replacing the ejected fluid includes means for adding fluid to the bounce chamber at a temperature and inan amount providing cooling of the bounce chamber during operation of the engine.

3. A free piston engine according to claim 1 in which said venting passage means is opened to said bounce chamber during an intermediate portion of said relative reciprocal movement while the bounce chamber approaches its minimum volume and is closed to said bounce chamber during the final portion of said relative movement in which the bounce chamber reaches its minimum volume thereby further increasing the bounce chamber pressure during said final portion of said relative movement and accordingly storing further energy by compression of said fluid in preparation for a return stroke. V I

4. A free piston engine according to claim 3 in which said venting passage is opened to said bounce chamber during an intermediate portion of the last half of the relative movement of the bounce piston in the direction of increasing pressure in the bounce chamber.

5. A free piston engine according to claim 3 in which said venting passage and said means selectively opening the venting passage includes a passage located at a lower inner surface of said bounce cylinder at a point passed by a lower edge of said bouncer piston during a limited portion of its compression stroke, thereby utilizing said piston to scrape solid and liquid contaminants along said lower surface to said venting passage for controlled high velocity ejection of pressurized fluid and entrained contaminants through said passage.

6. A free piston engine according to claim 1 in which said venting passage opens into and connects two axially spaced portions of said cylinder, said bounce piston has at least one sealing ring moving with itand engaging said cylinder, and said sealing ring moves along said cylinder from a first sealing position spaced from both of said cylinder portions toward one end of the cylinder to an intermediate venting position between said spaced cylinder portions, to a second sealing position spaced from both said cylinder portions toward the opposite end of the cylinder, said sealing ring thereby constituting at least part of the means selectively opening said venting passage to said bounce chamber during said limited portion of movement.

7. A free piston engine having, in combination, a power piston, a bounce compressor including a bounce cylinder, a bounce piston within the bounce cylinder and defining at least one bounce chamber therein, one of the bounce cylinder and bounce piston being operatively connected to the power piston whereby the bounce cylinder and bounce piston are relatively and reciprocally movable with respect to each other to control the movement of the power piston during operation of the engine, and improved venting and control means for said bounce chamber, said venting and control means including venting'passage means for communicating with a fluid discharge region and designed to communicate with the one bounce chamber in only certain positions of the bounce piston, and fluid controlling means for selectively controlling the communication of the venting passage means with the one bounce chamber, said fluid controlling means being effective to connect the venting passage means with the bounce chamber during a portion of the cycle of relative movement of the bounce piston and cylinder in which the pressure in the bounce chamber has increased, thereby providing a brief high velocity ejection of fluid and contaminants from the bounce chamber through the venting passage means, and said fluid controlling means and venting passage means having a cooperating construction and relative location limiting the high velocity ejection to only a small portion of the fluid compressed in the bouncer chamber and thereby maintaining sufficient pressure within the bounce chamber at the end of a bounce compression stroke to provide desired control of the power piston movement.

8. The apparatus of claim 7, including one-way control valve means positioned in the passage means to only allow the egress of fluid from the bounce chamber through the passage means.

9. The apparatus of claim 7, including one-way control valve means arranged relative to the bounce chamber to only allow the ingress of fluid into the bounce chamber, and including second passage means having one end communicating with the valve means and having another end arranged to communicate with a source of fluid to provide fresh fluid to the bounce chamber during a portion of the bounce compressor cycle.

10. In a free piston engine, a bounce compressor including: a bounce cylinder, a bounce piston reciprocally movable within and relative to the bounce cylinder and defining at least one bounce chamber in the bounce cylinder, passage means communicating with a fluid discharge region and designed to communicate with the one bounce chamber in certain positions of the bounce piston, and fluid controlling means for selectively controlling the communication of the passage means with the one bounce chamber including sealing means positioned around the bounce piston between the bounce piston and the adjacent wall of the bounce cylinder, the fluid controlling means being effective during a portion of the cycle of relative movement of the bounce piston to connect the passage means withthe bounce chamber to vent the bounce chamber and allow fluid along with any contaminants therein to flow to the fluid discharge region, wherein the fluid controlling means includes at least one slot formed in the bounce cylinder and extending longitudinally of the bounce cylinder, and wherein the bounce piston includes connection means and the passage means is formed within the bounce piston with a first end of the passage means formed in the side of the bounce piston and a second end of the passage means formed in the connection means to allow fluid communication from the bounce chamber to the fluid discharge region when the position of the bounce piston causes the first end of the passage to align with the slot. I

11. The apparatus of claim 10, wherein the sealing means comprises at least one sealing ring carried by the bounce piston between the first end of the passage means and the bounce chamber, and wherein the slot is of sufficient length to bypass the sealing ring carried by the bounce piston during a portion of the cycle of the bounce compressor to allow fluid communication between the first bounce chamber and the fluid discharge region during that portion of the cycle of the bounce compressor.

12. The apparatus of claim 11, wherein the bounce piston carries at least two sealing rings spaced from each other to form a second bounce chamber between the sealing rings and between the bounce piston and the adjacent wall of the bounce cylinder, wherein the length of the slot is sufficient to bypass the sealing ring adjacent the first bounce chamber but less than required to bypass both sealing rings, and wherein the first end of the passage means is positioned in the bounce piston adjacent the second bounce chamber.

13. The apparatus of claim 12, including one-way control valve means positioned in the passage means to only allow the egress of fluid from the second bounce chamber.

14. The apparatus of claim 13, wherein the bounce piston includes second one-way control valve means positioned adjacent the first bounce chamber and arranged to only allow the ingress of fluid into the first bounce chamber, and wherein the bounce piston and the connection'means include second passage means having a first end communicating with the second valve means and having a second end arranged to communicate with a source of fluid to allow fresh fluid to enter the first bounce chamber during a portion of the bounce compressor cycle.

15. The apparatus of claim 14, wherein a first cavity is formed within the bounce piston with a first end of the first cavity communicating with the second bounce chamber and a second end of the first cavity communicating with the first end of the first passage means; wherein the first one-way control valve means comprises a ball check valve assembly positioned in the first cavity and including an adjustable retaining ring positioned within the first cavity near the first end, a valve seat being formed in the side of the retaining ring adjacent the second end, including a ball positioned in the valve seat, and including a valve spring having one end in contact with the ball and having the other end in contact with the second end of the first cavity for applying a force to the ball tending to maintain the ball in the valve seat unless force applied to the ball by the pressure differential between the fluid discharge region and the second chamber overcomes the force applied by the valve spring to allow fluid from the second chamber to flow into the fluid discharge region; wherein a second cavity is formed within the bounce piston with a first end of the second cavity communicating with the first chamber and a second end of the second cavity communicating with the first end of the second passage; and wherein the second one-way control valve means comprises a second ball check valve assembly positioned in the second cavity and including a valve seat formed in the bounce piston adjacent the second end of the second cavity, including a ball positioned in the valve seat, including a retaining ring positioned in the bounce piston adjacent the first end of the second cavity, and including a valve spring having one end in contact with the retaining ring and the other end in contact with the ball for applying a force to the ball tending to maintain the ball in the valve seat unless the force .applied to the ball by the pressure differential between the source of fluid and the first chamber overcomes the force applied by the valve spring to allow fluid from the source of fluid to flow into the first chamber.

16. The apparatus of claim 12 wherein the bounce piston has first and second faces, the first face being adjacent the first bounce chamber, wherein the bounce piston defines a third bounce chamber in the bounce cylinder, the third bounce chamber being defined adjacent the second face of the bounce piston, and wherein the apparatus includes at least one second slot formed in the housing and extending longitudinally of the bounce cylinder, the second slot being longitudinally spaced from the first slot and being of sufficient length to bypass the sealing ring adjacent the third bounce chamber but shorter than required to bypass both sealing rings, the second slot venting the third bounce chamber during a portion of the cycle of the bounce compressor for allowing the venting of at least a part of any contaminants within the third bounce chamber.

17. The apparatus of claim 16, including one-way control valve means positioned adjacent the third bounce chamber and arranged to only allow entrance of fluid into the third bounce chamber to allow fresh fluid to flow into third chamber during a portion of the bouncer compressor cycle.

18. In a free piston engine, a bounce compressor including: a bounce cylinder, a bounce piston reciprocally movable within and relative to the bounce cylinder anddefining at least one bounce chamber in the bounce cylinder, passage means communicating with a fluid discharge region and designed to communicate withthe one bounce chamber in certain positions of the bounce piston, and fluid controlling means for selectively controlling the communication of the passage means with the one bounce chamber including sealing means positioned around the bounce piston between the bounce piston and the adjacent wall of the bounce cylinder, the fluid controlling means being effective during a portion of the cycle of relative movement of the bounce piston to connect the passage means with the bounce chamber to vent the bounce chamber and allow fluid along with any contaminants therein to flow to the fluid discharge region, wherein the sealing means includes first and second axially spaced sealing means between the piston and the bounce cylinder, the first sealing means being adjacent the bounce chamber and the second sealing means being axially spaced from the bounce chamber; wherein the bounce piston defines a second chamber in the bounce cylinder, the second chamber being defined adjacent the second sealing means of the bounce piston at the opposite axial side of the second sealing means 

1. In a free piston engine, a bounce compressor including a bounce cylinder, a bounce piston within the bounce cylinder and defining at least one bounce chamber therein, one of the bounce cylinder and bounce piston being operatively connected to the engine whereby the bounce cylinder and bounce piston are relatively and reciprocally movable with respect to each other to provide desired control requirements of the engine during operation, and improved venting and control means for said bounce chamber, said venting and control means including venting passage means of restricted cross section, and fluid controlling means selectively opening said venting passage means to said bounce chamber during only a limited portion of that half of the relative reciprocal movement of said piston and cylinder in which the bounce chamber pressure has increased, the venting passage means and fluid controlling means having a construction and relative arrangement and location providing, during said limited portion of movement, a brief, controlled high-velocity ejection of a small portion of fluid from said chamber through said venting passage means at a velocity and location providing effective removal of contaminants from said chamber with said fluid while maintaining sufficient compression pressure in the bounce chamber at the end of a bounce compression stroke to provide desired control requirements of the engine, and means for replacing the ejected fluid.
 2. A free piston engine according to claim 1 in which said means for replacing the ejected fluid includes means for adding fluid to the bounce chamber at a temperature and in an amount providing cooling of the bounce chamber during operation of the engine.
 3. A free piston engine according to claim 1 in which said venting passage means is opened to said bounce chamber during an intermediate portion of said relative reciprocal movement while the bounce chamber approaches its minimum volume and is closed to said bounce chamber during the final portion of said relative movement in which the bounce chamber reaches its minimum volume thereby further increasing the bounce chamber pressure during said final portion of said relative movement and accordingly storing further energy by compression of said fluid in preparation for a return stroke.
 4. A free piston engine according to claim 3 in which said venting passage is opened to said bounce chamber during an intermediate portion of the last half of the relative movement of the bounce piston in the direction of increasing pressure in the bounce chamber.
 5. A free piston engine according to claim 3 in which said venting passage and said means selectively opening the venting passage includes a passage located at a lower inner surface of said bounce cylinder at a point passed by a lower edge of said bouncer piston during a limited portion of its compression stroke, thereby utilizing said piston to scrape solid and liquid contaminants along said lower surface to said venting passage for controlled high velocity ejection of pressurized fluid and entrained contaminants through said passage.
 6. A free piston engine according to claim 1 in which said venting passage opens into and connects two axially spaced portions of said cylinder, said bounce piston has at least one sealing ring moving with it and engaging said cylinder, and said sealing ring moves along said cylinder from a first sealing position spaced from both of said cylinder portions toward one end of the cylinder to an intermediate venting position between said spaced cylinder portions, to a second sealing position spaced from both said cylinder portions toward the opposite end of the cylinder, said sealing ring thereby constituting at least part of the means selectively opening said venting passage to said bounce chamber during said limited portion of movement.
 7. A free piston engine having, in combination, a power piston, a bounce compressor including a bounce cylinder, a bounce piston within the bounce cylinder and defining at least one bounce chamber therein, one of the bounce cylinder and bounce piston being operatively connected to the power piston whereby the bounce cylinder and bounce piston are relatively and reciprocally movable with respect to each other to control the movement of the power piston during operation of the engine, and improved venting and control means for said bounce chaMber, said venting and control means including venting passage means for communicating with a fluid discharge region and designed to communicate with the one bounce chamber in only certain positions of the bounce piston, and fluid controlling means for selectively controlling the communication of the venting passage means with the one bounce chamber, said fluid controlling means being effective to connect the venting passage means with the bounce chamber during a portion of the cycle of relative movement of the bounce piston and cylinder in which the pressure in the bounce chamber has increased, thereby providing a brief high velocity ejection of fluid and contaminants from the bounce chamber through the venting passage means, and said fluid controlling means and venting passage means having a cooperating construction and relative location limiting the high velocity ejection to only a small portion of the fluid compressed in the bouncer chamber and thereby maintaining sufficient pressure within the bounce chamber at the end of a bounce compression stroke to provide desired control of the power piston movement.
 8. The apparatus of claim 7, including one-way control valve means positioned in the passage means to only allow the egress of fluid from the bounce chamber through the passage means.
 9. The apparatus of claim 7, including one-way control valve means arranged relative to the bounce chamber to only allow the ingress of fluid into the bounce chamber, and including second passage means having one end communicating with the valve means and having another end arranged to communicate with a source of fluid to provide fresh fluid to the bounce chamber during a portion of the bounce compressor cycle.
 10. In a free piston engine, a bounce compressor including: a bounce cylinder, a bounce piston reciprocally movable within and relative to the bounce cylinder and defining at least one bounce chamber in the bounce cylinder, passage means communicating with a fluid discharge region and designed to communicate with the one bounce chamber in certain positions of the bounce piston, and fluid controlling means for selectively controlling the communication of the passage means with the one bounce chamber including sealing means positioned around the bounce piston between the bounce piston and the adjacent wall of the bounce cylinder, the fluid controlling means being effective during a portion of the cycle of relative movement of the bounce piston to connect the passage means with the bounce chamber to vent the bounce chamber and allow fluid along with any contaminants therein to flow to the fluid discharge region, wherein the fluid controlling means includes at least one slot formed in the bounce cylinder and extending longitudinally of the bounce cylinder, and wherein the bounce piston includes connection means and the passage means is formed within the bounce piston with a first end of the passage means formed in the side of the bounce piston and a second end of the passage means formed in the connection means to allow fluid communication from the bounce chamber to the fluid discharge region when the position of the bounce piston causes the first end of the passage to align with the slot.
 11. The apparatus of claim 10, wherein the sealing means comprises at least one sealing ring carried by the bounce piston between the first end of the passage means and the bounce chamber, and wherein the slot is of sufficient length to bypass the sealing ring carried by the bounce piston during a portion of the cycle of the bounce compressor to allow fluid communication between the first bounce chamber and the fluid discharge region during that portion of the cycle of the bounce compressor.
 12. The apparatus of claim 11, wherein the bounce piston carries at least two sealing rings spaced from each other to form a second bounce chamber between the sealing rings and between the bounce piston and the adjacent wall of the bounce cylinder, wherein the length of the slot is sufficient to bypass tHe sealing ring adjacent the first bounce chamber but less than required to bypass both sealing rings, and wherein the first end of the passage means is positioned in the bounce piston adjacent the second bounce chamber.
 13. The apparatus of claim 12, including one-way control valve means positioned in the passage means to only allow the egress of fluid from the second bounce chamber.
 14. The apparatus of claim 13, wherein the bounce piston includes second one-way control valve means positioned adjacent the first bounce chamber and arranged to only allow the ingress of fluid into the first bounce chamber, and wherein the bounce piston and the connection means include second passage means having a first end communicating with the second valve means and having a second end arranged to communicate with a source of fluid to allow fresh fluid to enter the first bounce chamber during a portion of the bounce compressor cycle.
 15. The apparatus of claim 14, wherein a first cavity is formed within the bounce piston with a first end of the first cavity communicating with the second bounce chamber and a second end of the first cavity communicating with the first end of the first passage means; wherein the first one-way control valve means comprises a ball check valve assembly positioned in the first cavity and including an adjustable retaining ring positioned within the first cavity near the first end, a valve seat being formed in the side of the retaining ring adjacent the second end, including a ball positioned in the valve seat, and including a valve spring having one end in contact with the ball and having the other end in contact with the second end of the first cavity for applying a force to the ball tending to maintain the ball in the valve seat unless force applied to the ball by the pressure differential between the fluid discharge region and the second chamber overcomes the force applied by the valve spring to allow fluid from the second chamber to flow into the fluid discharge region; wherein a second cavity is formed within the bounce piston with a first end of the second cavity communicating with the first chamber and a second end of the second cavity communicating with the first end of the second passage; and wherein the second one-way control valve means comprises a second ball check valve assembly positioned in the second cavity and including a valve seat formed in the bounce piston adjacent the second end of the second cavity, including a ball positioned in the valve seat, including a retaining ring positioned in the bounce piston adjacent the first end of the second cavity, and including a valve spring having one end in contact with the retaining ring and the other end in contact with the ball for applying a force to the ball tending to maintain the ball in the valve seat unless the force applied to the ball by the pressure differential between the source of fluid and the first chamber overcomes the force applied by the valve spring to allow fluid from the source of fluid to flow into the first chamber.
 16. The apparatus of claim 12 wherein the bounce piston has first and second faces, the first face being adjacent the first bounce chamber, wherein the bounce piston defines a third bounce chamber in the bounce cylinder, the third bounce chamber being defined adjacent the second face of the bounce piston, and wherein the apparatus includes at least one second slot formed in the housing and extending longitudinally of the bounce cylinder, the second slot being longitudinally spaced from the first slot and being of sufficient length to bypass the sealing ring adjacent the third bounce chamber but shorter than required to bypass both sealing rings, the second slot venting the third bounce chamber during a portion of the cycle of the bounce compressor for allowing the venting of at least a part of any contaminants within the third bounce chamber.
 17. The apparatus of claim 16, including one-way control valve means positioned adjacent the third bounce chamber and arRanged to only allow entrance of fluid into the third bounce chamber to allow fresh fluid to flow into third chamber during a portion of the bouncer compressor cycle.
 18. In a free piston engine, a bounce compressor including: a bounce cylinder, a bounce piston reciprocally movable within and relative to the bounce cylinder and defining at least one bounce chamber in the bounce cylinder, passage means communicating with a fluid discharge region and designed to communicate with the one bounce chamber in certain positions of the bounce piston, and fluid controlling means for selectively controlling the communication of the passage means with the one bounce chamber including sealing means positioned around the bounce piston between the bounce piston and the adjacent wall of the bounce cylinder, the fluid controlling means being effective during a portion of the cycle of relative movement of the bounce piston to connect the passage means with the bounce chamber to vent the bounce chamber and allow fluid along with any contaminants therein to flow to the fluid discharge region, wherein the sealing means includes first and second axially spaced sealing means between the piston and the bounce cylinder, the first sealing means being adjacent the bounce chamber and the second sealing means being axially spaced from the bounce chamber; wherein the bounce piston defines a second chamber in the bounce cylinder, the second chamber being defined adjacent the second sealing means of the bounce piston at the opposite axial side of the second sealing means from the bounce chamber and first sealing means; and wherein the fluid controlling means includes slot means positioned in the bounce cylinder and extending longitudinally of the bounce cylinder, the slot means arranged to bypass both of the first and second sealing means during a portion of the bounce compressor cycle to provide fluid communication between the first bounce chamber and the second chamber. 